Method of enhancing surface reactions by local resonant heating

ABSTRACT

Methods and an apparatus for processing a substrate. A first method comprising: reacting a layer formed on the substrate with a plasma to form a reaction product layer; and simultaneously exposing the reaction product layer to resonant radiation to volatilize the reaction product layer. A second method comprising: performing a plasma enhanced chemical vapor deposition to deposit a precursor layer on a substrate; and simultaneously heating the precursor layer by exposure of the precursor layer to resonant radiation to convert the precursor layer to a deposited layer.

FIELD OF THE INVENTION

[0001] The present invention relates to the field of plasma processing; more specifically, it relates to a method for plasma etching and plasma enhanced deposition and apparatus for plasma etching and plasma enhanced deposition.

BACKGROUND OF THE INVENTION

[0002] In plasma based processing, high-energy electrons are used to convert neutral molecules in the gas phase to charged ions and neutral free radicals. Typically, the gas phase temperature is less than 500° C., whereas the electron cloud has energy equivalent to a temperature in excess of 10,000° C. The ambipolar field resulting from the difference in mobility of the electrons and ions generates an anistropic flux of energetic ions (and neutrals via charge exchange collisions) to the surface of the substrate being processed. This flux, in combination with an isotropic flux of reactive neutral free radicals, either etches material from the surface or deposits material on the surface.

[0003] Simultaneous with the surface chemistry, there is a proportional heating of the surface and heating of the substrate itself, both from plasma radiation and bulk heat applied. If the wafer heating is to high, then damage to structures within the substrate occurs. If the wafer temperature or flux of energetic ions or reactive neutral free radicals is to low, then processing times increase as reaction rates decrease. Increasingly, when plasma processing is applied to advanced materials, no satisfactory compromise between wafer heating, which impacts yield and thus cost, and reaction rates, which impacts, productivity and thus cost, can be found.

SUMMARY OF THE INVENTION

[0004] A first aspect of the present invention is a method of processing a substrate comprising: reacting a layer formed on the substrate with a plasma to form a reaction product layer; and simultaneously exposing the reaction product layer to resonant radiation to volatilize the reaction product layer.

[0005] A second aspect of the present invention is a method of processing a substrate comprising: performing a plasma enhanced chemical vapor deposition to deposit a precursor layer on a substrate; and simultaneously heating the precursor layer by exposure of the precursor layer to resonant radiation to convert the precursor layer to a deposited layer.

[0006] A third aspect of the present invention is an apparatus for processing a substrate, the apparatus comprising: a chamber; a process gas distribution system adapted to distribute one or more process gases into the chamber; means for generating a plasma from the one or more process gases, the plasma capable of processing a layer on the substrate; a substrate support within the chamber adapted to hold the substrate to expose a top surface of the substrate to the plasma; a resonant radiation source adapted to expose the layer to resonant radiation; and an exhaust adapted to remove volatilized reaction products from the chamber.

BRIEF DESCRIPTION OF DRAWINGS

[0007] The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

[0008]FIG. 1 is a plot of vapor pressure of CuCl₂ versus temperature.

[0009]FIG. 2 is a schematic diagram illustrating a plasma etch process according to the present invention.

[0010]FIG. 3 is a schematic diagram illustrating a plasma-enhanced deposition according to the present invention.

[0011]FIG. 4 is a schematic diagram of a first plasma etch/deposition system according to the present invention;

[0012]FIG. 5 is a schematic diagram of a second plasma etch/deposition system tool according to the present invention;

[0013]FIG. 6A is a schematic diagram of a prismatic infrared radiation source;

[0014]FIG. 6B is a schematic diagram of a grating based infrared radiation source; and

[0015]FIG. 6C is a schematic diagram of a tunable laser infrared radiation source.

DETAILED DESCRIPTION OF THE INVENTION

[0016]FIG. 1 is a plot of vapor pressure of CuCl₂ versus temperature. In a plasma etch process, gas phase reactant species (free radicals and ions) are formed in the plasma. The reactant species then strike on a surface of a substrate and chemically react with the surface. The reaction rate is directly related to the volatility (partial pressure) of the product of the reaction (if the product is not removed then the surface becomes coated with reaction product, effectively blocking fresh reactants from reaching un-reacted material). An example of such a process is the etching of copper in chlorine. In the plasma, chlorine free radicals and chlorine ions are created (plasma activation), the chlorine free radicals and ions strike on a copper surface and form copper chloride (ion surface activation) which is a solid. Then the copper chloride is converted to a gas (volatilization) due to heat generated from the reaction, radiant heat from the plasma or bulk heating of the substrate. This set of reactions may be written:

Plasma Activation: Cl₂→2Cl⁺+2e   (1)

Ion Surface Activation: Cu+Cl+Cl⁺→CuCl₂(s)   (2)

Volatilization (>600° C.): CuCl₂(s)+Δ→CuCl₂↑  (3)

[0017] In FIG. 1, it can be seen that a temperature of about 750° C. is required to produce a partial vapor pressure of CUCl₂ of about 1 Torr. As the temperature decreases the partial pressure of CuCl₂ decreases. At less than 600° C., the partial pressure of CuCl₂ is so low (only a couple of hundredths of a Torr) that the surface is effectively passivated and no further reaction can occur. Therefore, there is a temperature P_(T), which is the optimum temperature for plasma etching copper in chlorine. However, there may be a maximum temperature W_(T), which the substrate can be allowed to reach. In FIG. 1 W_(T) is indicated as being a temperature of about 300-400° C. At 300-400° C., the vapor pressure of CuCl₂ is essentially zero and no volatilization of CuCl₂ will occur so the reaction rate will be essentially zero. For example, in etching copper films on silicon wafers containing sensitive MRAM devices(magnetic random access memory devices) the wafer temperature cannot exceed 250° C. For CMOS (complimentary metal oxide silicon) devices, the wafer temperature cannot exceed 300 to 350° C. due to thermal budgets required to protect diffusion portions of the transistors.

[0018] In the present invention, an additional process step (resonant heating) is added that locally heats the CuCl₂ formed, but not a significant portion of the surrounding copper film. The reactions for this process may be written:

Plasma Activation: Cl₂→2Cl⁺+2e   (1)

Ion Surface Activation: Cu+Cl+Cl⁺→CuCl₂(s)   (2)

Resonant Heating: CuCl₂(s)+hv→[CuCl₂(s)]_(E)   (4)

Volatilization (>600° C.): [CUCl₂(s)]_(E)+δΔ→CuCl₂↑  (5)

[0019] The resonant heating is accomplished by supplying electromagnetic energy (radiation) at a wavelength (or frequency) that will couple to and thus excite of one of the vibrational states of CuCl₂. In equation (4), “h” is Planck's constant and “v” is frequency. Therefore, resonant radiation is defined as radiation having a wavelength that will couple with a vibrational state of the material exposed to the resonant radiation. Resonant heating is discussed more fully infra. Thus, in reaction (4) the CuCl₂ (s) is resonant heated so that the heat (δΔ) required in reaction (5) for volatilization of the excited CuCl₂ is only a fraction of the heat required (Δ) in reaction (3) for volatilization of the CuCl₂.

[0020] This allows for either a lower temperature plasma process to be used or aggressive cooling of the wafer to be performed. Sufficient electromagnetic energy may be supplied so that the resonant heating is all that is required and the CuCl₂ volatilizes as reaction (4) occurs.

[0021] Examples of other metals that may be plasma etched according to the present invention are platinum and iron. The reactions for Pt may be written:

Plasma Activation: Cl₂→2Cl⁺+2e   (6)

Ion Surface Activation: Pt+Cl⁺→PtCl (s)   (7)

Resonant Heating: PtCl (s)+hv→[PtCl (S)]_(E)   (8)

Volatilization (>600° C.): [PtCl (S)]_(E)+δΔ→PtCl (s)↑  (9)

[0022] The reactions for iron are similar, except the minimum volatilization temperature for iron chloride is greater than 900° C. Other metals and non-metallic films may also be etched according to the present invention

[0023]FIG. 2 is a schematic diagram illustrating a plasma etch process according to the present invention. In FIG. 2, formed on a substrate 100 is an insulator layer 105. Formed on insulator 105 is a copper layer 110. Formed on etchable layer 110 is a masking layer 115. Trenches 120 are being etched in etchable layer 110. A reaction product layer 125 is continuously formed and removed at the bottom of each trench 120 so each trench becomes increasingly deeper. Reactant species X as well as electromagnetic energy hv strike on masking layer 115 and etchable layer 110. The material of masking layer 115 is chosen to not react with reactant species X or vibrationally couple with electromagnetic energy hv. However, reactant species X is chosen to react with etchable layer 110 to form reaction product layer 125 and the wavelength of electromagnetic energy hv is chosen to vibrationally couple with the reaction product layer and hence heat the reaction product layer to sufficiently high enough temperature to volatilize the reaction product layer into vaporized reaction product Z. The amount and wavelengths of electro-magnetic energy hv is discussed infra.

[0024] Regions 130 in etchable layer 110 near the bottom 135 of each trench 120 define the extent of local radiant heating caused by the coupling of electromagnetic energy hv with reaction product layer 125. The temperature of regions 130 is less than the volatilization temperature of reaction product layer 125. If the temperature of reaction product layer 125 is T1, the temperature of region 130 is T2 and the temperature of substrate 100 is T3, then the following relationship holds: T1>T2>T3.

[0025] In one example, masking layer 115 is plasma enhanced chemical vapor deposition (PECVD) oxide, etchable layer 110 is Cu, Pt or Fe and the reactant species X is Cl free radicals/ions.

[0026] Turning to how much energy most be supplied by electromagnetic energy hv, a relatively straightforward approximation may be made. A 300 mm diameter wafer with 50% exposed etchable layer (Cu in a Cl₂ system in the present example) is assumed and the heat of vaporization of the reaction product, heat of formation of the reaction product and general plasma induced heating is assumed to be provided by the reactive plasma flux. The reactive area is 0.5π(150×10⁻¹ m)² and given an etch rate of 2E10⁻⁹ m/s, the volume rate of CuCl₂ removal is 0.07 mm³/s. This translates into a mole removal rate of CuCl₂ of (8.92 g/cm³)×(1 mole/98.9 g)×(0.07 mm³/s)=6.2×10⁻⁶ mole/s. Given that ΔH=CpΔT×mole, where ΔH is enthalpy, Cp=48.7 J/K mole is the heat capacity of copper and ΔT=500° K. (the assumed difference between CuCl₂ volatilization temperature and the wafer temperature), then ΔH=0.15 Joules/s=150 mW. Given half the source energy is directed away from the wafer (as in the etch system illustrated in FIG. 4 and described infra) a 300 mW source for a 300 mm diameter wafer=0.42 mW/cm² is required.

[0027] Turning to how the wavelength of electromagnetic energy hv is determined, and continuing the CUCl₂ example, it can be seen from Table I that 5 possible wavelengths, corresponding to five transition energies of CuCl₂ could be used. TABLE I CuCl₂ Vibrational Coupling Transition Energy Wavelength cm⁻¹ μm Designation 9567.5 1.04 Near IR 6877 1.45 Near IR 1910.9 5.2 Mid IR 364.5 27.4 Mid IR 98.6 101.4 Far IR

[0028] Turning to sources of infrared (IR) energy, and continuing the CuCl₂ example, it can be seen from Table II that at least four possible IR sources could be used that give the requisite 0.42 mW/cm² of spectral radiance using a 5 nm bandpass filter. The bandpass filter is required to filter wavelengths that would couple with materials other than CuCl₂. TABLE II Spectral radiance Source Radiating Wavelength (mW cm-2, with 5 nm Type material range band pass filter) Nerst Zirconia, yittria or  0.4-20 μm 1 Glower thoria at 1200-2000° K Globar SiC at    1-40 μm 1 1300-1500° K Tungsten Tungsten 0.3-2.5 μm 100 2000-3000° K Xeon Arc High Pressure   0.2-1 μm 1000 (>10 Torr Xe)

[0029] All the sources in Table II belong to the class of sources known as broadband sources.

[0030]FIG. 3 is a schematic diagram illustrating a plasma-enhanced deposition according to the present invention. The principles of the present invention described supra in relation to plasma etching are applicable to PECVD processing as well. The example of silicon oxide deposition will be used. In FIG. 3, being formed on a substrate 140 is SiO₂ layer 145. Being formed on SiO₂ layer 145 is a precursor (SiH₃)₂O layer 150 formed from (SiH₃)₂O precipitate formed in the gas phase plasma. The chemical name of (SiH₃)₂O is silicyl oxide. (SiH₃)₂O layer 150 is continuously be transformed into SiO₂ layer 145 as the deposition continues by resonant heating caused by electro-magnetic energy hv impinging on the newly formed (SiH₃)₂O layer 150 and subsequent release of H₂O and H₂. The reactions for SiO₂ deposition according to the present invention may be written:

Plasma Activation: SiH₄+e→SiH₃+H   (10A)

N₂O+e→>NO+O   (10B)

Surface Precipitate: 2 SiH₃+O→(SiH₃)₂O (s)   (11)

Precursor Resonant Heating: (SiH₃)₂O (s)+hv→(SiH₃)₂O (s)   (12)

Volatilization (>600° C.): (SiH₃)₂O (s)+5 O→2 SiO₂+H₂↑+2 H₂O↑  (13)

[0031] While precursor (SiH₃)₂O layer 150 is resonantly heated to at least 600° C., under laying SiO₂ layer 145 does not absorb a significant amount of this resonant radiation. Since (SiH₃)₂O layer 150 can be heated to very high temperatures the resultant PECVD SiO₂ has properties similar to low pressure high temperature chemical vapor deposition (LPCVD) SiO₂. Other materials, for example silicon nitride, may be deposited according to the present invention.

[0032]FIG. 4 is a schematic diagram of a first plasma etch/deposition system according to the present invention. In FIG. 4, plasma etch/deposition system 200 includes a chamber 205, a wafer chuck 210, solenoidal coils 215, a transmissive window 220 in a top 225 of chamber 205, an optional bandpass filter 230 and IR sources 235. A wafer 240 is located on a top surface 245 of wafer chuck 210. Chamber 205 is fitted with a reactant gas supply 250 and an exhaust 255. A radio frequency (RF) power supply 260A is coupled between solenoidal coils 215 and ground in order to strike and maintain a plasma 265 and an RF bias power supply 260B is coupled between wafer chuck 210 and ground in order to control forward bias (etch) power. IR source 235 generates infrared radiation 270, which passes through optional bandpass filter 230 and window 220 to strike a top surface 275 of wafer 240 wherein the infrared radiation couples with the reaction products of either the plasma etch or PECVD process being performed in chamber 205 as described in reference to FIGS. 2 and 3 and described supra.

[0033] IR source 235 may be one selected from Table II or another source, for example, a tunable IR laser. Bandpass filter 230 is not required in the cases of monochromatic IR sources (i.e. tunable IR laser) but only when broadband sources (i.e. those listed in table II) are used. Alternative radiation/wavelength selection sub-systems are illustrated in FIGS. 6A, 6B and 6C and described infra. Table III lists some suitable window materials. TABLE III Window Material Wavelength Sapphire (Al₂O₃) 0.17-5.5 μm Germanium  1.8-23 μm Silicon  1.2-15 μm Quartz  0.4-3 μm Silver Bromide 0.45-35 μm Rubidium Bromide 0.45-35 μm

[0034] The choice of window material is a function of the resonant IR wavelength selected and the plasma reaction selected. E.g. the window must pass the required frequency and not be attacked by the plasma process.

[0035] Process parameters for a typical non-volatile metal etch process (i.e. Cu, Pt, Fe, etc.) that may be run in plasma etch/deposition system 200 include (for 8 inch wafers and scalable for 12 inch wafers) a Cl₂ flow rate of 160 sccm, an Ar flow rate of 40 sccm, a BCL₃ flow rate of 13 sccm, chamber pressure of 36 mT, a wafer temperature of 375° C., RF power of 900-1200 watts and bias power of 450 watts.

[0036] Examples of commercial plasma systems that may be modified to practice the present invention (i.e. addition of window 220, optional filter 230, and IR source 235) include, but are not limited to, the AMAT DPS etch system and the AMAT HDP deposition system both manufactured by Applied Materials Corporation, Santa Clara, Calif.

[0037]FIG. 5 is a schematic diagram of a second plasma etch/deposition system according to the present invention. In FIG. 5, plasma etch/deposition system includes a chamber 305, a wafer chuck 310, plate 315, a transmissive window 320 in a sidewall 325 of chamber 305, an optional bandpass filter 330 and IR sources 335. A wafer 340 is located on a top surface 345 of wafer chuck 310. Chamber 305 is fitted with a reactant gas supply 350 and an exhaust 355. An RF power supply 360A is coupled between plate 315 and ground in order to strike and maintain a plasma 365 and an RF bias power supply 360B is coupled between wafer chuck 310 and ground in order to control forward bias (etch) power. IR source 335 generates infrared radiation 370, which passes through optional bandpass filter 330 and window 320 to strike a top surface 375 of wafer 340 wherein the infrared radiation couples with the reaction products of either the plasma etch or PECVD process being performed in chamber 305 as described in reference to FIGS. 2 and 3 and described supra.

[0038] IR source 335 may be one selected from Table II or another source, for example, a tunable IR laser. Bandpass filter 330 is not required in the cases of monochromatic IR sources (i.e. tunable IR laser) but only when broadband sources (i.e. those listed in table II) are used. Alternative radiation/wavelength selection sub-systems are illustrated in FIGS. 6A, 6B and 6C and described infra. Table III supra lists some suitable window materials.

[0039] Process parameters for a typical silane based oxide deposition process (i.e. Cu, Pt, Fe, etc.) that may be run in plasma etch/deposition system 300 include (for 8 inch wafers and scalable for 12 inch wafers) a SiH₄ flow rate of 300 sccm, a N₂ flow rate of 1500 sccm, a N₂O flow rate of 9500 sccm, chamber pressure of 2400 mT, a wafer temperature of 400° C., a plate power of 1100 watts and wafer chuck power of 0 watts (no wafer chuck power).

[0040] Examples of commercial plasma systems that may be modified to practice the present invention (i.e. addition of window 320, optional filter 330, and IR source 335) include, but are not limited to, the LAM research 2300 etch system manufactured by Lam Research, Fremont, Calif., and the Novellus PECVD system manufactured by Novellus Corporation, San Jose, Calif.

[0041]FIG. 6A is a schematic diagram of a prismatic infrared radiation source. In FIG. 6A, an IR source 400 generates polychromatic IR radiation 405, which is dispersed into its component wavelengths 410 by a prism 415. A resonant wavelength (actually range of wavelengths) 420 is selected by tunable wavelength selection window 425. IR source 400 may be selected from Table II supra. Suitable prism material and their wavelength ranges are listed in Table IV. TABLE IV Prism Material Wavelength SiO₂ 0.25-2 μm LiF 0.2-5 μm CaF 0.2-9 μm BaF2 0.2-13 μm NaCl 2-16 μm KBr 10-25 μm CsI 15-50

[0042]FIG. 6B is a schematic diagram of a grating based infrared radiation source. In FIG. 6B, an IR source 430 generates polychromatic IR radiation 435, which is dispersed into its component wavelengths 440 by a grating 445. A resonant wavelength 450 (actually range of wavelengths) is selected by tunable wavelength selection window 455. IR source 430 may be selected from Table II supra. Suitable prism material and their wavelength ranges are listed in Table V. TABLE IV Grating Density Grooves/mm Wavelength 300-600 0.8-2.5 μm 100-300 2.5-50 μm  30-100 50-1000 μm

[0043]FIG. 6C is a schematic diagram of a tunable laser infrared radiation source. In FIG. 6B, an tunable laser IR source 460 generates narrow beam monochromatic IR radiation 465, which is dispersed into a wide beam monochromatic IR radiation 470 by a dispersing reflector 475.

[0044] The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention. 

What is claimed is:
 1. A method of processing a substrate comprising: reacting a layer formed on said substrate with a plasma to form a reaction product layer; and simultaneously exposing said reaction product layer to resonant radiation to volatilize said reaction product layer.
 2. The method of claim 1, further including: maintaining said substrate at a first temperature, said first temperature lower than a second temperature required to volatilize said reaction product.
 3. The method of claim 1, wherein said resonant radiation does not couple with said layer.
 4. The method of claim 1, wherein said resonant energy is infrared radiation.
 5. The method of claim 1, wherein said layer includes a first material selected from the group consisting of copper, platinum, and iron and said reaction layer includes a second material selected from the group consisting of copper chloride, platinum chloride, and iron chloride.
 6. The method of claim 1, wherein said plasma includes chlorine species.
 7. The method of claim 1, further including: forming a masking layer on a top surface of said layer, said layer exposed through holes formed in said masking layer.
 8. A method of processing a substrate comprising: performing a plasma enhanced chemical vapor deposition to deposit a precursor layer on a substrate; and simultaneously heating said precursor layer by exposure of said precursor layer to resonant radiation to convert said precursor layer to a deposited layer.
 9. The method of claim 8, further including: maintaining said substrate at a first temperature, said first temperature lower than a second temperature required to convert said precursor layer to said deposited layer.
 10. The method of claim 8, wherein said resonant radiation does not couple with said precursor layer.
 11. The method of claim 8, wherein said precursor layer includes silicyl oxide and said deposited layer includes silicon dioxide.
 12. An apparatus for processing a substrate, the apparatus comprising: a chamber; a process gas distribution system adapted to distribute one or more process gases into said chamber; means for generating a plasma from said one or more process gases, said plasma capable of processing a layer on said substrate; a substrate support within said chamber adapted to hold said substrate to expose a top surface of said substrate to said plasma; a resonant radiation source adapted to expose said layer to resonant radiation; and an exhaust adapted to remove volatilized reaction products from said chamber.
 13. The apparatus of claim 12, wherein said processing said layer either etches said layer or deposits said layer.
 14. The apparatus of claim 12, further including a window formed in a top of said chamber or a sidewall of said chamber, said window substantially transparent to said resonant radiation.
 15. The apparatus of claim 14, wherein said resonant radiation source is external to said chamber and aligned to expose said layer to said resonant radiation through said window.
 16. The apparatus claim 14, wherein said window includes material selected from the group consisting of sapphire, germanium, silicon, quartz, silver bromide and rubidium bromide.
 17. The apparatus of claim 15, further including means for selecting a range of wavelengths for said resonant radiation, said means for selecting position between said resonant radiation source and said window.
 18. The apparatus of claim 17, wherein said means for selecting a range of wavelengths includes a prism and a tunable wavelength selection window or a grating and said tunable wavelength selection window.
 19. The apparatus of claim 12, wherein said resonant radiation source is an infrared source selected from the group consisting of Nerst glowers, globars, tungsten filaments, xenon arcs, broadband infrared sources and tunable infrared lasers.
 20. The method of claim 12, wherein said means for generating a plasma includes exposing said one or more process gases to radio frequency radiation. 